setting a recaptcha theme for use in Blog

OK, I have recaptch working in my new blog (very easy to setup, nice). Anyway I want to change the look of the recaptcha. I read the api info on thier site, and the docs here http://doc.silverstripe.org/doku.php?id=modules:recaptcha
The reference to: $recaptchaField->jsOptions = array('theme' => 'clean'); // optional
looks promising, but there isn't any real followup info/deatils.
Can this method be used with the blog/forum intergration?
Where are the 'theme' settings set?, I couldn't find any templates for recaptcha.. and I am unsure what 'clean' refers to.
also how would this be added to mysite/_config.php?

UPDATE OK, after digging deeper I now see a reference to: Note: Only available if {@link $useJavascript} is turned on.
in the RecaptchaField.php file..

How can I set this? Sorry.. I am pretty new to some of this.. any help would be appreciated.